Measurement of the dynamic characteristics of interferometric modulators

ABSTRACT

Various systems and methods of lighting a display are disclosed. In one embodiment, for example, a method includes applying a voltage waveform to the interferometric modulators, applying a voltage pulse to the interferometric modulators, detecting reflectivity of light from the interferometric modulators, and determining one or more quality parameters of the interferometric modulators based on the detecting reflectivity of light, where the applied voltage pulse causes the interferometric modulators to vary between an actuated and a non-actuated state, or an non-actuated state and an actuated state.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/613,537 titled “Measurement of the Dynamic Characteristics ofInterferometric Modulators,” filed Sep. 27, 2004, which is incorporatedby reference in its entirety and assigned to the assignee of the presentinvention.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS).

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. It would be beneficial to beable to measure parameters of the interferometric modulators indicativeof their performance to determine whether they are adequate for aparticular application. Testing the performance of the MEMSinterferometric modulator before it is incorporated in a display productis useful for discovering fabrication problems and identifying defectivemodulators early in the manufacturing process of the display product.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

In another embodiment, a method of testing a plurality ofinterferometric modulators includes applying a voltage waveform to theinterferometric modulators to vary the interferometric modulatorsbetween an actuated and a non-actuated state, or an non-actuated stateand an actuated state, detecting light related from the interferometricmodulators, and determining one or more response time parameters of theinterferometric modulators based on said detecting.

In another embodiment, a system for testing a plurality ofinterferometric modulators, comprises, an illumination source adapted toprovide incident light to a plurality of interferometric modulators, avoltage source adapted to apply a voltage waveform to theinterferometric modulators to vary the interferometric modulatorsbetween an actuated and a non-actuated state, or an non-actuated stateand an actuated state, an optical detector adapted to detect lightreflected from the plurality of interferometric modulators and produce asignal corresponding to the detected light, and a computer configured toreceive the signal from the optical detector and determine one or moreresponse time parameters of the interferometric modulators based on thesignal.

In another embodiment, a system for testing a plurality ofinterferometric modulators, comprises means for providing light to theplurality of interferometric modulators, means for applying a voltagewaveform to the interferometric modulators to vary the interferometricmodulators between an actuated and a non-actuated state, or annon-actuated state and an actuated state, means for detecting lightreflected from the plurality of interferometric modulators, means forproducing a signal corresponding to the detected light, and means fordetermining one or more response time parameters of the interferometricmodulators based on the signal.

In another embodiment, a method of testing a plurality ofinterferometric modulators comprises applying a voltage waveform to theinterferometric modulators to vary the interferometric modulatorsbetween an actuated and a non-actuated state, or an non-actuated stateand an actuated state, detecting reflectivity of light from theinterferometric modulators, and determining one or more response timeparameters of the interferometric modulators based on said detectingreflectivity of light, wherein said determining step determines anactuation time of at least a portion of the interferometric modulatorsduring application of the positive switching voltage level.

In another embodiment, a system of testing a plurality ofinterferometric modulators comprises a voltage source configured toapply a voltage waveform to the interferometric modulators to vary theinterferometric modulators between an actuated and a non-actuated state,or an non-actuated state and an actuated state, a light sourcepositioned to illuminate the interferometric modulators, a detectordisposed to receive light from the interferometric modulators andproduce a corresponding signal, and a computer configured to receive thesignal from the detector and determine, based on the signal, one or moreresponse time parameters of the interferometric modulators duringapplication of an actuation voltage or a release voltage.

In another embodiment, a system for testing a plurality ofinterferometric modulators comprises means for applying a voltagewaveform to the interferometric modulators to vary the interferometricmodulators between an actuated and a non-actuated state, or annon-actuated state and an actuated state, means for illuminating theinterferometric modulators, means for sensing light reflected from theinterferometric modulators and producing a corresponding signal, andmeans for determining, based on the signal, one or more response timeparameters of the interferometric modulators during application of anactuation voltage or a release voltage.

In another embodiment, a method of testing a plurality ofinterferometric modulators comprises setting a time period during whichto apply a switching voltage level, said switching voltage level beingsufficient to change the interferometric modulators between anon-actuated state and an actuated state, or an actuated state and anon-actuated state, applying a voltage waveform comprising the switchingvoltage level for the time period, detecting light reflecting from theinterferometric modulators, determining one or more response timeparameters of the interferometric modulators based on said detecting,and repeating said setting, applying, detecting, and determining step toidentify a minimum time period where a sufficient number of pixels haveactuated or released, wherein said subsequent setting of the time periodis done based on one or more determined response time parameters.

In another embodiment, a system for testing a plurality ofinterferometric modulators comprises a computer configured to determinea time period during which to apply a switching voltage level, saidswitching voltage level being sufficient to change the interferometricmodulators between a non-actuated state and an actuated state, or anactuated state and a non-actuated state, a voltage source controlled bysaid computer, said voltage source configured to apply a voltagewaveform comprising the switching voltage level for the time period, alight source positioned to illuminate the interferometric modulators,and a detector positioned to receive light reflecting from theinterferometric modulators and produce a signal corresponding to thereceived light, wherein said computer receives the signal from thedetector and determines one or more response time parameters based onthe signal, and said computer is further configured to iterativelycontrol the application of a voltage waveform for a determined timeperiod to identify a minimum time period where the number of pixels haveactuated or released during the determined time period meets a thresholdvalue.

In another embodiment, a system for testing a plurality ofinterferometric modulators comprises means for determining a time periodduring which to apply a switching voltage level, said switching voltagelevel being sufficient to change the interferometric modulators betweena non-actuated state and an actuated state, or an actuated state and anon-actuated state; means for applying a controlled by said computer,said voltage source configured to apply a voltage waveform comprisingthe switching voltage level for the time period, means for illuminatingthe interferometric modulators; and means for sensing light reflectedfrom the interferometric modulators and produce a signal correspondingto the received light, wherein said determining a time period meansreceives the signal from the sensing means and determines one or moreresponse time parameters based on the signal, and said determining atime period means is further configured to iteratively control theapplication of a voltage waveform for a determined time period toidentify a minimum time period where the number of pixels have actuatedor released during the determined time period meets a threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view schematically depicting a portion of oneembodiment of an interferometric modulator display in which a movablereflective layer of a first interferometric modulator is in a relaxedposition and a movable reflective layer of a second interferometricmodulator is in an actuated position.

FIG. 2 is a system block diagram schematically illustrating oneembodiment of an electronic device incorporating a 3×3 interferometricmodulator display.

FIG. 3 is a schematic diagram of movable mirror position versus appliedvoltage for one exemplary embodiment of an interferometric modulator ofFIG. 1.

FIG. 4 is a schematic illustration of a set of row and column voltagesthat may be used to drive an interferometric modulator display.

FIGS. 5A and 5B schematically illustrate one exemplary timing diagramfor row and column signals that may be used to write a frame of displaydata to the 3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams schematically illustrating anembodiment of a visual display device comprising a plurality ofinterferometric modulators.

FIG. 7A is a schematic cross section of the device of FIG. 1.

FIG. 7B is a schematic cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a schematic cross section of another alternative embodimentof an interferometric modulator.

FIG. 7D is a schematic cross section of yet another alternativeembodiment of an interferometric modulator.

FIG. 7E is a schematic cross section of an additional alternativeembodiment of an interferometric modulator.

FIG. 8 is a schematic illustrating a system for visually observingreflectance of MEMS interferometric modulators.

FIG. 9 is a schematic illustrating a system for automaticallydetermining reflectance of MEMS interferometric modulators.

FIG. 10 is a schematic illustrating another embodiment of a system forautomatically determining reflectance of MEMS interferometricmodulators.

FIG. 11 is a schematic illustrating observing portions of an array ofMEMS interferometric modulators.

FIG. 12 is a graph illustrating a driving voltage for MEMSinterferometric modulators and the resulting reflectance of themodulators.

FIG. 13 is a graph illustrating an optical response of a MEMSinterferometric modulators.

FIG. 14 is a schematic illustrating a another graphical waveform used todrive MEMS interferometric modulator pixels to determine a qualitycharacteristic and a resulting optical response.

FIG. 15 is a flowchart illustrating a process for determining a responsetime of MEMS interferometric modulators.

FIG. 16A is a schematic graphically illustrating a waveform used todrive interferometric modulators to determine a response time.

FIG. 16B is a schematic illustrating graphically illustrating an opticalresponse of the interferometric modulators.

FIG. 17A is a schematic graphically illustrating a waveform used todrive interferometric modulators to determine a response time.

FIG. 17B is a schematic graphically illustrating an optical response ofthe interferometric modulators.

FIG. 18 is a flowchart illustrating a process for determining a minimumresponse time of MEMS interferometric modulators.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout.

As will be apparent from the following description, the embodiments maybe implemented in any device that is configured to display an image,whether in motion (e.g., video) or stationary (e.g., still image), andwhether textual or pictorial. More particularly, it is contemplated thatthe embodiments may be implemented in or associated with a variety ofelectronic devices such as, but not limited to, mobile telephones,wireless devices, personal data assistants (PDAs), hand-held or portablecomputers, GPS receivers/navigators, cameras, MP3 players, camcorders,game consoles, wrist watches, clocks, calculators, television monitors,flat panel displays, computer monitors, auto displays (e.g., odometerdisplay, etc.), cockpit controls and/or displays, display of cameraviews (e.g., display of a rear view camera in a vehicle), electronicphotographs, electronic billboards or signs, projectors, architecturalstructures, packaging, and aesthetic structures (e.g., display of imageson a piece of jewelry). MEMS devices of similar structure to thosedescribed herein can also be used in non-display applications such as inelectronic switching devices.

Testing the performance of interferometric modulators beforeincorporating them in a display product is useful for discoveringfabrication problems and identifying defective modulators early in themanufacturing process of the display product. In some embodiments, theoperation of an array of interferometric modulators is tested to ensureit meets response time appropriate criteria for its intended use.Generally, the response time is the length of time it takes theinterferometric modulators to change from an actuated state to areleased state, or vice-versa, in response to an appropriate appliedvoltage signal.

In some embodiments, the operation of the array of interferometricmodulators is tested by detecting the light reflected from the arraywhile setting the interferometric modulators to an actuated or releasedstate. By first determining threshold values that associate the amountof reflected light with the number of interferometric modulators thathave actuated or released, a response time of the array ofinterferometric modulators can be determined by applying a drivingvoltage that causes the array of interferometric modulators to changestate, and determining how long it takes for the pre-determined numberof interferometric modulators to change state, based on the lightreflected from the array. The reflected light is detected eithervisually by an operator or automatically (e.g., by a computerizedinspection system). Measuring the actuation and release response time isespecially important when the interferometric modulators are going to beused in a device that requires relatively fast refresh rates, forexample, displaying image data at a video data rate. In typicalapplications for testing response times for multiple interferometricmodulators the measured response time reflects the slowest response ofthe variables that affect response time.

One way to measure a response time is to first apply an offset voltageto the interferometric modulators to ensure they are in a releasedstate, and then an actuation voltage is applied. In another test, anoffset voltage is first applied to release the interferometricmodulators, then a bias voltage is applied, and finally an actuationvoltage is applied, thus testing a response time in the manner theinterferometric modulators and typically operated (e.g., within ahysteresis window). For both of the tests, the actuation voltage isapplied for a relatively long period of time compared to the responsetime. Alternatively, the length of time that an actuation (or release)voltage is applied can be varied to determine the minimum amount of timerequired to actuate (or release) a predetermined number ofinterferometric modulators.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable highlyreflective layer 14 b is illustrated in an actuated position adjacent tothe optical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto anoptically transmissive (e.g. transparent) substrate 20. In someembodiments, the layers are patterned into parallel strips, and may formrow electrodes in a display device as described further below. Themovable reflective layers 14 a, 14 b may be formed as a series ofparallel strips of a deposited metal layer or layers (orthogonal to therow electrodes of 16 a, 16 b) deposited on top of posts 18 and anintervening sacrificial material deposited between the posts 18. Whenthe sacrificial material is etched away, the movable reflective layers14 a, 14 b are separated from the optical stacks 16 a, 16 b by a definedgap 19. A highly conductive and reflective material such as aluminum maybe used for the reflective layers 14, and these strips may form columnelectrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in FIG. 1) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2-5 illustrate one exemplary process and system for using an arrayof interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias). As is also illustrated in FIG.4, it will be appreciated that voltages of opposite polarity than thosedescribed above can be used, e.g., actuating a pixel can involve settingthe appropriate column to +V_(bias), and the appropriate row to −ΔV. Inthis embodiment, releasing the pixel is accomplished by setting theappropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel. As isalso illustrated in FIG. 4, it will be appreciated that voltages ofopposite polarity than those described above can be used, e.g.,actuating a pixel can involve setting the appropriate column to+V_(bias), and the appropriate row to −ΔV. In this embodiment, releasingthe pixel is accomplished by setting the appropriate column to−V_(bias), and the appropriate row to the same −ΔV, producing a zerovolt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 44, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one oremore devices over a network. In one embodiment the network interface 27may also have some processing capabilities to relieve requirements ofthe processor 21. The antenna 43 is any antenna known to those of skillin the art for transmitting and receiving signals. In one embodiment,the antenna transmits and receives RF signals according to the IEEE802.11 standard, including IEEE 802.11(a), (b), or (g). In anotherembodiment, the antenna transmits and receives RF signals according tothe BLUETOOTH standard. In the case of a cellular telephone, the antennais designed to receive CDMA, GSM, AMPS or other known signals that areused to communicate within a wireless cell phone network. Thetransceiver 47 pre-processes the signals received from the antenna 43 sothat they may be received by and further manipulated by the processor21. The transceiver 47 also processes signals received from theprocessor 21 so that they may be transmitted from the exemplary displaydevice 40 via the antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure or heat-sensitive membrane.In one embodiment, the microphone 46 is an input device for theexemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the optically transmissive substrate 20, the sideopposite to that upon which the modulator is arranged. In theseembodiments, the reflective layer 14 optically shields the portions ofthe interferometric modulator on the side of the reflective layeropposite the substrate 20, including the deformable layer 34 and the busstructure 44. This allows the shielded areas to be configured andoperated upon without negatively affecting the image quality. Thisseparable modulator architecture allows the structural design andmaterials used for the electromechanical aspects and the optical aspectsof the modulator to be selected and to function independently of eachother. Moreover, the embodiments shown in FIGS. 7C-7E have additionalbenefits deriving from the decoupling of the optical properties of thereflective layer 14 from its mechanical properties, which are carriedout by the deformable layer 34. This allows the structural design andmaterials used for the reflective layer 14 to be optimized with respectto the optical properties, and the structural design and materials usedfor the deformable layer 34 to be optimized with respect to desiredmechanical properties.

The fabrication of a MEMS interferometric modulator may use conventionalsemiconductor manufacturing techniques such as photolithography,deposition (e.g., “dry” methods such as chemical vapor deposition (CVD)and wet methods such as spin coating), masking, and etching (e.g., drymethods such as plasma etch and wet methods), etc. Testing theperformance of the MEMS interferometric modulator before it isincorporated in a display product is useful for discovering fabricationproblems and identifying defective modulators early in the manufacturingprocess of the display product.

In some embodiments, the operation of an array of interferometricmodulators is tested by detecting the light reflected from the arraywhile setting the interferometric modulators to an actuated or releasedstate in a predetermined process, for example, those processes which aredescribed further herein. Such testing can be done to determine desiredquality checks, including to test the uniformity of the array in areleased or actuated state, or to determine the actuation and/or releaseresponse times. Depending on the testing methodology, the reflectedlight can be detected with either visually (e.g., by an operator) orautomatically (e.g., by a computerized inspection system). For example,FIG. 8 illustrates an embodiment of a system to inspect an array fordefect detection by visually inspecting the light reflected from anilluminated array while the array is being driven to various knownstates. A MEMS interferometric modulator array is placed in a probemount 102. The probe mount 102 is interfaced with a switch box 104and/or control computer 106 to control the driven states of the arrayusing drive schemes that are described hereinbelow. In some embodiments,a diffuser plate 108 may be placed over the array so that the viewer 110observes a non-specular display. A continuous spectrum light source 112can be provided to assist visual observation of the reflected light. Insome embodiments, multiple displays may be viewed by the viewer 110simultaneously to increase throughput. The systems and processesdisclosed herein for testing an array can also be used to test single ormultiple interferometric modulators that are not configured in an array.

In some embodiments, the testing process may be automated. Thus, forexample, detection of reflectivity as a function of applied voltagestimulus may be automatically performed at pre-determined areas on aninterferometric modulator array. The calculation of parameters andquality control determinations may be automatically performed usingsuitable algorithms executed on a computing device. Furthermore,positioning of interferometric modulator arrays within a testingapparatus may be automated so that high throughput of mass-manufacturedinterferometric modulator displays may be accomplished. In someembodiments, a selected percentage sample of mass-manufactured displaysare tested for quality control purposes.

One embodiment of an apparatus suitable for measuring the reflectivityof an array of interferometric modulators using an automated detectionsystem is depicted in FIG. 9. An array 120 that includes a plurality ofinterferometric modulators, for example, similar to the interferometricmodulator illustrated in FIG. 1, is electrically connected to a voltagedriving source 122. The voltage driving source 122 applies thetime-varying voltage stimulus, such as a square voltage waveform, to thearray 120. The voltage signal may be applied to all interferometricmodulators in the array 120 simultaneously. Alternatively, a voltagesignal may be applied to only those interferometric modulators fromwhich reflectivity are being measured. A light source 124 illuminatesthe array 120. In one embodiment, a standard D65 light source is usedfor the light source 124. Light source 124 provides light 126 to theinterferometric modulator array 120, which is then reflected upward.

A photo detector 128 may be used to detect the intensity of thereflected light 130 from the interferometric modulator array 120. Adiffuser film 132 may be optionally placed over the interferometricmodulator array 120. The diffuser film 132 scatters the light 130reflected from the interferometric modulator array 120. Such scatteringallows the light source 124 and detector 128 to be placed at angles 134and 136 relative to the array 120. While the incident light reflectedfrom the array 120 may be at a maximum if angles 134 and 136 arecomplementary, the use of a diffuser film 132 allows for detection at anangle differing from the angle of greatest specular reflection. If adiffuser film 132 is not used, then it can be advantageous that incidentlight 126 fall incident on and reflect back from the array 120 at anangle close to perpendicular to the array 120. Such a configuration isdesirable because interferometric modulators can have a narrow viewingangle causing the intensity of reflected light to fall rapidly at widerangles.

A computer 138 in communication with the detector 128 can be used torecord reflectivity versus voltage characteristics (e.g., the hysteresiscurve) and calculate electrical parameters. The computer 138 can beconnected to the voltage driving source 122 to provide interferometricmodulator response time information relative to the time when thedriving voltage is applied to the array 120. In typical applications fortesting response times for multiple interferometric modulators, forexample, an array of interferometric modulators, the measured responsetime reflects the slowest response of the variables that affect responsetime.

Because a MEMS interferometric modulator display is reflective andinherently specular in nature, it can be advantageous to detect ameasure of reflectance of the array of incident light and reflectedlight that are both normal to the substrate surface (e.g., in-linelighting). In one embodiment, in-line lighting is accomplished using asystem illustrated in FIG. 10. In this system, a beam splitter 150 isprovided that reflects light from a light source 152 onto the array 120being evaluated. The path of the light 126 reflected by the beamsplitter 150 is normal to the array 120. The voltage driving source 122applies a desired time-varying voltage stimulus to the array 120 whilethe light source 152 illuminates the array 120.

A detection module 128 is positioned to detect light 130 reflected fromthe array 120 and passing through the beamsplitter 150. In this way,both the incident light 126 and the reflected light 130 are normal tothe array 120. In some embodiments, the system may additionally comprisea microscope objective 154 for evaluating only a small portion of thetotal active surface area. The array 120 may be placed in probe mount156 which may then be secured to an X-Y stage 158 for moving the array120 so that the desired portion of the active area is under themicroscope objective 154 for evaluation. The detection module 128 maycomprise one or more detectors such as a photo detector or spectrometer,and a CCD camera 160.

One or more beam splitters 162 may be used for simultaneous measurementby more than one detector. The light source 152 may be chosen to providelight having the desirable spectral and intensity characteristics. Forexample, it may be desirable to have the light source 152 approximatethe characteristics of the light source that will typically be used toview a display the array 120 is intended to be incorporated in. In oneembodiment, a standard D65 light source is used. In some embodiments,the light source 152 may be coupled to an illumination control device164, preferably of the Koehler design. The aperture of the illuminationcontrol device 164 may be adjusted to illuminate only the area ofinterest on the array 120.

A computer 138 in communication with the detector 128 can be used torecord reflectivity versus voltage characteristics (e.g., the hysteresiscurve) and calculate parameters including response times of theinterferometric modulators. The computer 138 can be connected to thevoltage driving source 122 to provide interferometric modulator responsetime information relative to the time when the driving voltage isapplied to the array 120. In some embodiments, the computer 138 can alsobe used to control the driving voltage source 122 during testing ofinterferometric modulators.

Other embodiments of systems are available for achieving in-linelighting and detection. For example, in some embodiments a bundle offiber optics, some of which provide incident light and others whichdetect reflected light may be aligned over the desired area of array120. One or more fibers in the bundle may be connected to a light sourcewhile one or more other fibers in the bundle are connected to detectors.In one embodiment, multiple outer fibers in the bundle are connected toa light source while one or more inner fibers in the bundle areconnected to one or more detectors such as a spectrometer and/or aphotodetector. In some embodiments, the end of the fiber bundle ispositioned such that a beam splitter, such as beam splitter 150 in FIG.10, directs incident and reflected light normal to the array 120. Thisconfiguration allows additional detectors in detection module 128, suchas a CCD camera 160, to be used simultaneously. Alternatively, the fiberbundle may be positioned so that the end is already normal to the array120.

FIG. 11 depicts an interferometric modulator array 120 containing aplurality of interferometric modulator elements 202. As discussed above,a microscopic lens 154 may be used to focus detection of reflectivity ona portion of the interferometric modulator array 120 while the array isdriven using a desired voltage waveform, as discussed in reference toFIGS. 12-19. For example, area 204 may be the area that is detectedduring testing. The area 204 tested may be of any suitable size. In oneembodiment, only a few interferometric modulator elements 202 areincluded. In one embodiment, an approximately 1 mm diameter spot ismeasured. In some embodiments, multiple areas, such as areas 204, 206,208, 210, and 212 are measured sequentially on the same array 120. Thenumber of areas and location of the areas may be selected based on thedesired testing standard. For example, the suggested number of spotmeasurements and their locations recommended by ANSI or VESA for displaytesting may be used. In one embodiment, a single area 204 near thecenter of the array 120 is measured.

An optical system such as described above with reference to FIGS. 8-11may be used to characterize the electro-optical characteristics of oneor more pixels or regions of the array while it is driven to actuateand/or release. In one embodiment, the uniformity of bright and darkstates when the interferometric modulators are driven by a memorywaveform is measured. The entire array can be driven by a gang drivesuch that all interferometric modulators are driven together (e.g., allrows are shorted and grounded while all columns are shorted and driven).A region of the interferometric modulators array may be examined using,for example, the system described in FIG. 10 having a detector 128 andan analysis computer 138. In some embodiments, a viewer can asses theuniformity of bright and dark states by visually observing CCD images.Alternatively, analysis of the CCD images may be automated using acomputer algorithm.

In some embodiments, one or more memory characteristics of a pixel orregion are tested and/or measured by focusing the microscope objective230 on a single pixel, or a group of pixels, and adjusting the in-linelighting to illuminate that pixel or group. In other embodiments, one ormore memory characteristics of the entire array or a large region of thearray are tested. In some testing, it may be desirable to “gang” drivethe array by, for example, connecting all row leads to ground and allcolumn leads to the same voltage waveform, so that the entire group ofpixels or the array can exhibit the uniform reflectance characteristics.FIG. 12 exemplifies the actuation and release characteristics of oneembodiment of a gang driven array of interferometric modulators. Here,the memory characteristics are illustrated by driving the array with avoltage waveform 228. Hysteresis occurs because the voltage differentialrequired to actuate the modulators in the array is higher than a voltagerequired to maintain the modulators in their current state, which inturn is higher than the voltage required to release the modulators inthe array. Thus, there is a window of voltages where the array will notchange state even when the voltage is changed. FIG. 12 illustrates thedrive voltage 228 and the reflectance 230 from the array (e.g., asmeasured by the photodetector) as a function of time. Alternatively, theresponse may be depicted as a hysteresis plot as in FIG. 13, which plotsreflectivity as a function of drive voltage. A response that does notreveal the expected hysteresis shape of FIG. 13 will be indicative of ananomaly in the pixel or region of the array.

In some embodiments, the response of the interferometric modulators maybe characterized by four voltage levels: positive actuation (+Vact),positive release (+Vrel), negative actuation (−Vact), and negativerelease voltage (−Vrel). These voltage levels themselves are arbitraryas the actual positive actuation voltage, positive release voltage,negative actuation voltage, and negative release voltage will varydepending on the structure of the particular interferometric modulator.These voltage levels may be determined from the plots of FIG. 12 or 13.+Vact 220 corresponds to the voltage at which the MEMS interferometricmodulator will be driven from a released state to an actuated state asvoltage is increased. +Vrel 222 corresponds to the voltage at which theMEMS interferometric modulator will release from an actuated state whenthe voltage is decreased. −Vact 224 corresponds to the voltage at whichthe MEMS interferometric modulator will be driven from a released stateto an actuated state as voltage is decreased. −Vrel 226 corresponds tothe voltage at which the MEMS interferometric modulator will releasefrom an actuated state when the voltage is increased.

The appropriate parameters for setting up a memory waveform for sometesting processes can be determined using these four voltage levels.These parameters include the amplitude of bias (Vbias), the DC offsetvoltage (Voffset), the memory window (ΔVmem), and the pulse needed toactuate the pixel (Vact). In some embodiments, these parameters can bedetermined as follows:V _(bias)=[((+Vact++Vrel)/2)−((−Vact+−Vrel)/2)]/2V _(offset)=[((+Vact++Vrel)/2)+((−Vact+−Vrel)/2)]/2ΔVmem=Min[(+Vact−+Vrel),(−(−Vact−−Vrel)]Vact=2×+V _(bias)

With reference to FIG. 13, V_(bias) corresponds generally to the voltagethat the center of the memory window is offset from the symmetricalcenter of the hysteresis plot. V_(offset) corresponds generally to thevoltage that the symmetrical center is offset from 0V, for example, itis typically calculated as the average of the positive actuation voltage(+Vact) and the negative actuation voltage (−Vact). ΔVmem corresponds tothe voltage window in which the state of the interferometric modulatorwill not change. The actuation voltage corresponds to a potential thatwill ensure actuation of the interferometric modulator. These parametersmay be used to determine the appropriate control voltages for the arrayunder investigation or to determine whether the array will be suitablefor the desired application. For example, in a display application, amemory window (ΔVmem) of less than 0.5 V may indicate that the array hasfailed testing and cannot be used.

In one embodiment, the response time of a pixel or a region (e.g., aportion) of a MEMS interferometric modulator array (both of which arereferred to here as “the interferometric modulators”) can be measured byasserting a drive voltage step across the interferometric modulators andmeasuring the reflectance response using a photodetector. FIG. 14illustrates one example of a voltage waveform that includes such avoltage step. In FIG. 14, plot 300 is a graphical representationillustrating a drive voltage waveform as a function of time. Here, theasserted voltage waveform includes a voltage step 304 from a firstvoltage level 301 at about the offset voltage (Voff), at which theinterferometric modulators are in a released state, to a second voltagelevel 302 at a positive actuation voltage (Vact). Upon assertion of thisvoltage step, the interferometric modulators begin to change theirreflectance properties from a bright state (released) to a dark state(actuated). If the light reflecting from the interferometric modulatorsis detected during the application of this voltage step, a response timefor positive actuation (Tpa) can be determined by measuring the time ittakes for the interferometric modulators to achieve a certain change inreflectivity. The voltage step 308 from a positive actuation voltagelevel 302 to a release voltage level 306 allows a similar detection ofthe positive release response time (Tpr). Similarly, the negativeactuation (Tna) 314 and negative release (Tnr) 316 response times may bedetermined by detecting the reflected light while actuating theinterferometric modulators with a voltage step at a negative actuationvoltage (−Vact), and then while asserting a voltage level 316 whichreleases the interferometric modulators. The term “offset voltage” maybe used to describe the average of the positive actuation voltage(+Vact) and the negative actuation voltage (−Vact), illustrated in FIG.12. In typical applications for testing response times, the measuredresponse time reflects the slowest response of the testedinterferometric modulators.

An example of the reflectance that occurs when interferometricmodulators are actuated or released is depicted in the lower plot 310 ofFIG. 14. Here, the change in reflectance of the interferometricmodulators is shown as a function of time. A measure of the relativechange in reflectance can be used to illustrate both the change inreflectance from a bright (released) state to a dark (actuated) state,and the change from a dark state to a bright state. In one embodiment, aresponse time is defined as the time it takes the reflectance response312 of the interferometric modulators to reach a certain level of thetotal reflectance response as triggered by a voltage level change toactuate or release the interferometric modulators. In one embodiment, aresponse time is defined as the time it takes the reflectance response312 of the interferometric modulators to reach 90% of the totalreflectance response. In other embodiments, other percentages (orlevels) of reflectance less than 90% or greater than 90% can be used. Insome embodiments, the response time is repeatedly measured to determineits consistency. The criteria for an acceptable response time may varydepending on the application. For example, for display applications thatdo not require rapid changes in the picture displayed, a longer responsetime can be acceptable.

One skilled in the art will recognize that there are many alternativeembodiments of the voltage waveform depicted in FIG. 14. Depending onthe display application, the preferred embodiment for the response timewaveform may be altered to mimic the expected drive signals of the finaldisplay. The waveform illustrated in FIG. 14 is one example of awaveform that can be used for determining response times. In someembodiments, only a portion of the waveform is used, for example, afirst portion as indicated between numerals 301 and 306 can be used totest the positive actuation and release response times (positiverelative to the offset voltage). In some tests, this portion of thewaveform can be applied to the interferometric modulators multipletimes. In such cases, a period of this portion of the waveform can bedefined (e.g., between numerals 303 and 306) and a frequency of applyingthe waveform portion can also be defined. Similar periods andfrequencies can be defined for all the waveforms and/or portions ofwaveforms described herein. For example, another periodic waveform maybe defined between numerals 303 and 316, which includes both thepositive actuation and release with the negative actuation and release.In some applications, the waveforms, or portions thereof, are applied tothe interferometric modulators at a frequency of about 10 Hz-5000 Hz,depending on the response time being measured.

FIG. 15 is a flowchart of a process 330 for determining one or moreresponse time parameters of interferometric modulators. In state 332, avoltage waveform is applied to the array to change the state of thepixels from an actuated state to a released state, or from a releasedstate to an actuated state. To measure a response time, the voltagewaveform should be asserted long enough to allow the actuation orrelease of all the interferometric modulators, that is, the length oftime of asserting the voltage should be longer than the response time sothat the length of time is not a limiting factor to the response timemeasurement. In state 334, the reflectivity of the array is measuredrelative to the time of applying the voltage waveform using a detector.Then, in state 336, the process 330 determines one or more response timeparameters of the pixels based on the detected reflectance, for example,as illustrated in FIG. 14, or in FIGS. 16A and 16B. For some responsetime measurements, an actuation voltage is applied to theinterferometric modulators without when they are not subject to a biasvoltage (e.g., FIG. 14). Other response time measurements are made byapplying an actuation voltage to interferometric modulators that arefirst subject to a bias voltage (e.g., FIGS. 16A and 16B).

FIG. 16A is a graphical representation of a voltage waveform 380, as afunction of time, that can be used to drive one or more MEMSinterferometric modulators to determine a response time. FIG. 16B is agraphical representation of a corresponding measured reflectance 382 asa function of time from interferometric modulators driven by the voltagewaveform 380 shown in FIG. 16A. The voltage waveform 380 is showncentered at an offset voltage, which can be set at different voltagelevels in various embodiments of MEMS interferometric modulators and/ordrive schemes. Accordingly, the positive and negative bias voltages, andthe positive and negative actuation voltages are discussed relative tothe offset voltage, and do not imply that the voltages are necessarilypositive or negative relative to a ground voltage of zero.

In this embodiment, the actuation and release response times, bothpositive and negative, are determined for interferometric modulatorsthat are subject to a voltage level that is within the hysteresiswindow. At time 350, the voltage waveform is at a positive bias voltage(+Vbias) that is within the hysteresis window of the interferometricmodulators, the numerals herein relating to time referring to points intime as indicated along the x-axis (time). At time 352 the voltagewaveform 380 is set to the voltage offset, and then increased to thepositive bias voltage (+Vbias). Setting the voltage at the offsetvoltage ensures that the pixels are in a released state at time 354. Attime 356, the voltage is increased from the bias positive bias voltage(+Vbias) to a positive actuation voltage (+Vact) and held there for aduration of time delta t (Δt) which extends until time 358. When theactuation voltage is applied, the pixels correspondingly actuate over adiscrete time period causing the reflectance of the pixels to changefrom a bright state to a dark state. The actuation voltage, as well asthe bias voltage can vary depending on the configuration of theinterferometric modulators. In one example, the positive actuationvoltage is about two times the positive bias voltage level, and thenegative actuation voltage is about two times the negative bias voltagelevel.

FIG. 16B illustrates the change in reflectance 382 of theinterferometric modulators as a function of time, the time axis of FIG.16A corresponding with the time axis of FIG. 16B. As illustrated in FIG.16B, when the interferometric modulators are actuated at time 356, thereflectance changes, and the time during which the reflectance changesis the positive actuation response time (Tpa). The reflectance of thepixels can be measured by using a variety of systems, including one ofthe systems previously described herein.

In various embodiments, the response can be deemed complete when thereflectance decreases to certain thresholds, such as 90%, 95%, or 99% ofthe total reflectance response. Different thresholds may be appropriatefor the various displays that the pixels may be incorporated into. Thethresholds can be predetermined, or dynamically determined based on oneor more operating conditions or application requirements. The timeperiod Δt during which the actuation voltage is asserted is of arelatively large duration compared to the response time being measuredto ensure that any pixel that can actuate will actuate.

At time 360, the voltage is decreased to the offset voltage, which isthe release voltage for the pixels. When this occurs, the pixels releaseand the reflectance of the pixels increases. As illustrated in FIG. 16B,this time period during which the interferometric modulators release isthe positive release response time (Tpr). Similarly to the positiveactuation response time, the positive release response time can bedetermined by measuring the time period that it takes for thereflectance of the pixels to reach a certain threshold once the voltagehas been set to the offset voltage at time 360.

At time 364 the voltage waveform 380 is set to a negative bias voltage(−Vbias). Then at time 366, the voltage waveform 380 is set to anegative actuation voltage (−Vact) to actuate the interferometricmodulators. When the voltage is changed from −Vbias to −Vact at time366, the pixels are actuated so that they become darker, and thenegative actuation response time (Tna) can be determined based onmeasuring the reflectance of the pixels. When the voltage is changedfrom −Vbias to the offset voltage at time 370, the pixels are releasedand their reflectance increases as they change to a bright state.Similarly to the other response time measurements described here, thenegative release response time (Tnr) can be determined based onmeasuring how long it takes for the change in reflectance of theinterferometric modulators to reach a certain threshold. FIG. 16B alsoillustrates the negative actuation time (Tna) and the negative releasetime (Tna) which corresponds to the negative actuation at time 366 andthe negative release at time 370, respectively. The response timesdetermined here are based on the interferometric modulators beingoperated with hysteresis, for example, the response times are based onchanging the voltage from a voltage that is within the hysteresiswindow, e.g., +Vbias, to a voltage outside the hysteresis window, e.g.,+Vact. By actuating and releasing the interferometric modulators whenthey are subject to a voltage level within the hysteresis window, thepixels are tested under operating conditions that may closer mimic theiractual operating conditions.

Referring now to FIGS. 17A and 17B, in another embodiment the actuationand release response times are calculated for MEMS interferometricmodulators by varying the length of the time Δt of applying theactuation voltage (positive or negative) while monitoring the pixels todetermine when they have actuated or released. The time period Δt isvaried until a minimum time value is determined during which anacceptable number (or percentage) of the pixels are able to actuate (orrelease) within that minimum time period. This process is referred toherein as the “minimum time line process.”

FIG. 17A illustrates a voltage waveform 480 generally similar to thevoltage wave 380 shown in FIG. 16A. However, the voltage waveform 480,or a portion thereof (e.g., the positive or negative actuation voltageportion) is applied to the interferometric modulators multiple times,and each time a response time is determined based on detecting lightreflecting from the interferometric modulators, as previously described.The length of time during which an actuation voltage is applied can bevaried to determine a minimum time to apply the actuation voltage thatstill allows the interferometers to actuate, illustrated in FIG. 17B byΔt₁ and Δt₃. Similarly, the length of time during which a releasevoltage is applied can be varied to determine a minimum time forapplying the release voltage that still allows the interferometers torelease, illustrated in FIG. 17B by Δt₂ and Δt₄. These minimum times(Δt₁, Δt₂, Δt₃, and Δt₄) are long enough for the modulators to respondproperly to applied voltages. If the time Δt₁ is too short, thereflectance curve 482 will look like the first dotted line 483 becausethe modulators are not able to respond to a positive actuation voltage.One procedure is to increase the time Δt₁ during which an actuationvoltage is applied until actuation is observed, for example, either byan observer viewing the actuation or by a measurement system. Similarly,if the time Δt₃ is too short, the reflectance curve 482 will look likethe third dotted line 485 because the modulators did not respond to thenegative actuation voltage, and if the times Δt₂ or Δt₄ are too short,the reflectance curve 482 will look like the second and fourth dottedlines 484, 485 because the modulators will not respond to the appliedrespective positive or negative release voltages. These times (Δt₂, Δt₃,and Δt₄) can also be increased until the desired response is observed.

FIG. 17B illustrates on method of using the minimum time line process todetermine all response times by analyzing the reflectance verses timeplot shown as solid trace 482. The actuation and/or release of thepixels can be detected by various means, including by detecting thereflectance of the pixels using one of the systems described herein, oranother suitable system. The perceived or measured actuation or releaseindicates the actuation or release of the slowest respondinginterferometric modulator(s). The reflectance is measured to determineif certain reflectance thresholds are met, indicating that certainacceptable percentage of the pixels are actuating or releasing. In someembodiments, the determined acceptable threshold value of the percentageof pixels that actuate and/or release is 90% or higher, and in otherembodiments the percentage can be lower than 90%, e.g., 80%.

The minimum time line process is advantageously used to determine pixelresponse times when the pixels are going to be used in a device thatrequires fast refresh rates, for example, displaying image data at avideo data rate, because it allows for qualitative measurements that canbe standardized. Using a standardized value can also facilitate itsimplementation and various manufacturers.

FIG. 18 is a flowchart that illustrates a process 400 of testing aplurality of interferometric modulator pixels. In state 402, the process400, sets a time period during which to apply an actuation voltagelevel, the actuation voltage level being sufficient to change theinterferometric modulators between a non-actuated state and an actuatedstate, or an actuated state and a non-actuated state. In state 404 avoltage waveform that includes the actuation voltage for the duration ofthe time period is applied to the pixels. In state 406, the reflectivityof the pixels is detected and used to determine a sufficient number ofpixels are actuated or released. In state 408, a response time parameterof the pixels is determined based on the detected reflected light. Nextthe process in state 410 repeats the setting, applying, detecting, anddetermining step to identify a minimum time period where a sufficientnumber of pixels have actuated or released, wherein said subsequentsetting of the time period is done based on one or more determinedresponse time parameters.

As described above, visual observation or a measurement of thereflectance of the interferometric modulators can be used to determine aquality parameter. For example, in some testing the uniformity of theinterferometric modulators when they are all driven to an actuation orrelease state is evaluated, or in other testing the actuation or releaseresponse times of the interferometric modulators is determined. Inanother embodiment, the quality parameter can be determined by using thecolor response of the interferometric modulators, for example, by usingthe change in contrast to determine when the interferometric modulatorsare actuated or released, the uniformity of the actuation or releaserelative to time, or the actuation or release response times. The colorresponse of the array 120 of interferometric modulators can be detectedfrom the reflected light 130 and measured using a system similar to FIG.10, where the detector 128 comprises a spectrometer. The system, such asdescribed above, may be adjusted to focus on a single pixel or area ofthe array 120. It may be advantageous when testing a single pixel thatholes, posts, and any masking in the array not be included in the testarea. In one embodiment, the array is connected to a gang drive, such asdescribed above.

Color measurements can then be made under a variety of stimuluswaveforms. In one embodiment, the interferometric modulators aremeasured in both an undriven state and under a driving memory waveform,such as described above. Both bright and dark states under the drivingmemory waveform may be spectrally measured. Color information collectedfrom reflected light 130 may be converted to color parameters, forexample, the X, Y, Z CIE color tri-stimulus values. Because Y in the X,Y, Z CIE color tri-stimulus values contains all luminance information,the ratio of Ybright (e.g., non-actuated) to Ydark (e.g., actuated)provides a contrast ratio for contrast characterization, which can beused to determine a measure of uniformity similarly to reflectance. Insome embodiments, one or more of the color measurements are madeseparately. In some embodiments, this measurement is performed byilluminating the interferometric modulators with different coloredillumination sources and measuring the light reflected by each source.In other embodiments, the reflected light passes through a predeterminedfilter to select the desired wavelength to be measured.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A method of testing a plurality of interferometric modulators, themethod comprising: applying a voltage waveform to the interferometricmodulators to change the state of the interferometric modulators betweenan actuated and a released state, or a released state and an actuatedstate; detecting light reflected from the interferometric modulators asa function of time while applying said voltage waveform; and determiningat least one response time parameters of the interferometric modulatorsbased on said detecting, wherein the at least one parameter comprisesone of the following: a positive actuation response time (Tpa), anegative actuation response time (Tna), a positive release response time(Tpr), and a negative release response time (Tnr).
 2. The method ofclaim 1, wherein said applying comprises applying the voltage waveformat a frequency of between 10 Hz and 5000 Hz.
 3. The method of claim 2,wherein said applying comprises applying the voltage waveform at afrequency of between 50 Hz and 500 Hz.
 4. The method of claim 3, whereinsaid applying comprises applying the voltage waveform at a frequency ofbetween 50 Hz and 150 Hz.
 5. The method of claim 4, wherein saidapplying comprises applying the voltage waveform at a frequency of about100 Hz.
 6. The method of claim 1, wherein the waveform is appliedsimultaneously to all interferometric modulators.
 7. The method of claim1, wherein said detecting comprises detecting the light reflected fromless than all interferometric modulators.
 8. The method of claim 1,wherein said detecting comprises measuring the reflected light with aphotodetector.
 9. The method of claim 1, wherein said detectingcomprises measuring the reflected light through a diffuser positioned infront of the interferometric modulators.
 10. The method of claim 1,wherein said detecting comprises measuring the reflected light at anangle that is substantially perpendicular to the interferometricmodulators.
 11. The method of claim 1, wherein the voltage waveformcomprises a first portion at about an offset voltage level and a secondportion at an actuation voltage level.
 12. The method of claim 1,wherein the amplitude of the waveform is less than about 2 times thevoltage necessary to cause an actuation of the interferometricmodulators.
 13. The method of claim 12, wherein the amplitude of thewaveform is about 1.25 times the voltage necessary to cause an actuationof the interferometric modulators.
 14. The method of claim 1, whereinthe voltage waveform comprises a first portion at an actuation voltagelevel and a second portion at about an offset voltage level.
 15. Themethod of claim 1, wherein the response time parameters are based on theslowest response time of one or more of the plurality of interferometricmodulators.
 16. The method of claim 1, wherein each of the plurality ofinterferometric modulators comprises a fixed reflective surface and amoveable reflective surface wherein the fixed reflective surface and themoveable reflective surface are configured to cause interference oflight.
 17. A system for testing a plurality of interferometricmodulators, comprising: an illumination source adapted to provideincident light to a plurality of interferometric modulators; a voltagesource configured to apply a voltage waveform to the interferometricmodulators to vary the interferometric modulators between an actuatedand a released state, or a released state and an actuated state; anoptical detector configured to detect light reflected from the pluralityof interferometric modulators and produce a signal corresponding to thedetected light; and a computer configured to receive the signal from theoptical detector and determine at least one response time parameters ofthe interferometric modulators based on the signal, wherein the at leastone parameter comprises one of the following: a positive actuationresponse time (Tpa), a negative actuation response time (Tna), apositive release response time (Tpr), and a negative release responsetime (Tnr).
 18. The system of claim 17, wherein said voltage source isfurther configured to apply the voltage waveform at a frequency ofbetween 10 Hz and 5000 Hz.
 19. The system of claim 18, wherein saidvoltage source is further configured to apply the voltage waveform at afrequency of between 50 Hz and 500 Hz.
 20. The system of claim 17,wherein said voltage source is further configured to apply the voltagewaveform at a frequency of between 50 Hz and 150 Hz.
 21. The system ofclaim 17, wherein the waveform is applied simultaneously to allinterferometric modulators.
 22. The system of claim 17, wherein saidoptical detector is further configured to detect the reflected lightwith a photodetector.
 23. The system of claim 17, wherein said opticaldetector is further configured to detect the reflected light bymeasuring the reflected light through a diffuser positioned in front ofthe interferometric modulators.
 24. The system of claim 17, wherein saidoptical detector is further configured to detect the reflected light bymeasuring the reflected light at an angle that is substantiallyperpendicular to the interferometric modulators.
 25. The system of claim17, wherein said computer receives a signal from said voltage sourceindicating when a voltage is applied to the interferometric modulators.26. The system of claim 17, wherein the one or more response timeparameters are based on the slowest response time of one or more of theplurality of interferometric modulators.
 27. The system of claim 17,wherein each of the plurality of interferometric modulators comprises afixed reflective surface and a movable reflective surface wherein thefixed reflective surface and the movable reflective surface areconfigured to cause interference of light.
 28. A system for testing aplurality of interferometric modulators, comprising: means for providinglight to the plurality of interferometric modulators; means for applyinga voltage waveform to the interferometric modulators to vary theinterferometric modulators between an actuated and a released state, ora released state and an actuated state; means for detecting lightreflected from the plurality of interferometric modulators; means forproducing a signal corresponding to the detected light; and means fordetermining at least one response time parameters of the interferometricmodulators based on the signal, wherein the at least one parametercomprises one of the following: a positive actuation response time(Tpa), a negative actuation response time (Tna), a positive releaseresponse time (Tpr), and a negative release response time (Tnr).
 29. Thesystem of claim 28, wherein the light providing means comprises abroad-band light source.
 30. The system of claim 28, wherein the voltageapplying means comprises a voltage source.
 31. The system of claim 28,wherein the detecting means comprises an optical detector.
 32. Thesystem of claim 28, wherein the detecting means comprises aspectrometer.
 33. The system of claim 28, wherein the signal producingmeans comprises an optical detector.
 34. The system of claim 28, whereinthe determining means comprises a computer configured to receive thesignal from the detecting means.
 35. The system of claim 28, wherein theone or more response time parameters are based on the slowest responsetime of one or more of the plurality of interferometric modulators. 36.The system of claim 28, wherein each of the plurality of interferometricmodulators comprises a fixed reflective surface and a movable reflectivesurface wherein the fixed reflective surface and the movable reflectivesurface are configured to cause interference of light.
 37. A method oftesting a plurality of interferometric modulators, the methodcomprising: applying a voltage waveform to the interferometricmodulators to vary the interferometric modulators between an actuatedstate and a released state, or a released state and an actuated statewherein the voltage applied to change the state of the interferometricmodulators is applied while the interferometric modulators are subjectto a bias voltage; detecting light reflected from the interferometricmodulators while applying the voltage waveform; and determining at leastone response time parameters of at least a portion of theinterferometric modulators based on said detecting the reflected light,wherein the at least one parameter comprises one of the following: apositive actuation response time (Tpa), a negative actuation responsetime (Tna), a positive release response time (Tpr), and a negativerelease response time (Tnr).
 38. The method of claim 37, wherein the oneor more response time parameters are based on the slowest actuation timeof one or more interferometric modulators.
 39. The method of claim 37,wherein said voltage waveform comprising a first portion a voltage levelto place the interferometric modulators in an actuated state, a secondportion at a bias voltage level and a third portion at a voltage levelsufficient to release the interferometric modulators.
 40. The method ofclaim 37, wherein said voltage waveform comprising a first portion avoltage level to place the interferometric modulators in a releasedstate, a second portion at a bias voltage level and a third portion at avoltage level sufficient to actuate the interferometric modulators. 41.The method of claim 37, wherein each of the plurality of interferometricmodulators comprises a fixed reflective surface and a movable reflectivesurface wherein the fixed reflective surface and the movable reflectivesurface are configured to cause interference of light.
 42. A system oftesting a plurality of interferometric modulators comprising: a voltagesource configured to apply a voltage waveform to the interferometricmodulators to vary the interferometric modulators between an actuatedand a released state, or a released state and an actuated state, a lightsource positioned to illuminate the interferometric modulators; adetector disposed to receive light from the interferometric modulatorsand produce a corresponding signal; and a computer configured to receivethe signal from the detector and determine, based on the signal, atleast one response time parameters of at least a portion of theinterferometric modulators during application of an actuation voltage ora release voltage, wherein the at least one parameter comprises one ofthe following: a positive actuation response time (Tpa), a negativeactuation response time (Tna), a positive release response time (Tpr), anegative release response time (Tnr).
 43. The system of claim 42,wherein the one or more response parameters are based on the slowestactuation time of one or more interferometric modulators.
 44. The systemof claim 42, wherein each of the plurality of interferometric modulatorscomprises a fixed reflective surface and a movable reflective surfacewherein the fixed reflective surface and the movable reflective surfaceare configured to cause interference of light.
 45. A system for testinga plurality of interferometric modulators comprising: means for applyinga voltage waveform to the interferometric modulators to vary theinterferometric modulators between an actuated and a released state, ora released state and an actuated state; means for illuminating theinterferometric modulators; means for sensing light reflected from theinterferometric modulators and producing a corresponding signal; andmeans for determining, based on the signal, at least one response timeparameters of the interferometric modulators during application of anactuation voltage or a release voltage, wherein the at least oneparameter comprises one of the following: a positive actuation responsetime (Tpa), a negative actuation response time (Tna), a positive releaseresponse time (Tpr), and a negative release response time (Tnr).
 46. Thesystem of claim 45, wherein the one or more response time parameters arebased on the slowest actuation time of one or more interferometricmodulators.
 47. The system of claim 45, wherein said applying meanscomprises a controllable voltage source.
 48. The system of claim 45,wherein said illuminating means comprises a light source.
 49. The systemof claim 45, wherein said sensing means comprises a photo detector. 50.The system of claim 45, wherein said determining means comprises acomputer.
 51. The system of claim 45, wherein each of the plurality ofinterferometric modulators comprises a fixed reflective surface and amovable reflective surface wherein the fixed reflective surface and themovable reflective surface are configured to cause interference oflight.
 52. A method of manufacturing a system for testing a plurality ofinterferometric modulators comprising: providing a voltage sourceconfigured to apply a voltage waveform to the interferometric modulatorsto vary the interferometric modulators between an actuated and areleased state, or released state and an actuated state; positioning alight source to illuminate the interferometric modulators; positioning adetector to receive light reflected from the interferometric modulatorsand produce a corresponding signal; and coupling a computer to thedetector, the computer configured receive the signal from the detectorto determine, based on the signal, at least one response time parametersof the interferometric modulators during application of an actuationvoltage or a release voltage, wherein the at least one parametercomprises one of the following: a positive actuation response time(Tpa), a negative actuation response time (Tna), a positive releaseresponse time (Tpr), and a negative release response time (Tnr).
 53. Themethod of claim 52, wherein each of the plurality of interferometricmodulators comprises a fixed reflective surface and a movable reflectivesurface wherein the fixed reflective surface and the movable reflectivesurface are configured to cause interference of light.
 54. A method oftesting a plurality of interferometric modulators, the methodcomprising: setting a time period during which to apply a switchingvoltage level, said switching voltage level being sufficient to changethe interferometric modulators between a released state and an actuatedstate, or an actuated state and a released state; applying a voltagewaveform comprising the switching voltage level for the time period;detecting light reflected from the interferometric modulators;determining one or more response time parameters of the interferometricmodulators based on said detecting; and repeating said setting,applying, detecting, and determining step to identify a minimum timeperiod during which a threshold value is achieved, the threshold valueindicated a pre-determined number of pixels have actuated or released.55. The method of claim 54, wherein the one or more response timeparameters are based on the slowest actuation time of one or moreinterferometric modulators.
 56. The method of claim 54, wherein thevoltage applied to charge the state of the interferometric modulators isapplied while the interferometric modulators are subject to a biasvoltage.
 57. The method of claim 54, wherein said detecting reflectedlight comprises visual analysis.
 58. The method of claim 54, whereinsaid detecting reflected light comprises receiving the light in anoptical system and measuring contrast.
 59. The method of claim 54,wherein determining one or more response time parameters comprisesdetermining an actuation response time.
 60. The method of claim 54,wherein determining one or more response time parameters comprisesdetermining a release response time.
 61. The method of claim 54, whereineach of the plurality of interferometric modulators comprises a fixedreflective surface and a movable reflective surface wherein the fixedreflective surface and the movable reflective surface are configured tocause interference of light.
 62. A system for testing a plurality ofinterferometric modulators, comprising: a computer configured todetermine a time period during which to apply a switching voltage level,said switching voltage level being sufficient to change a predeterminednumber of interferometric modulators between a released state and anactuated state, or an actuated state and a released state; a voltagesource controlled by said computer, said voltage source configured toapply a voltage waveform comprising the switching voltage level for thetime period; a light source positioned to illuminate the interferometricmodulators; and a detector positioned to receive light reflecting fromthe interferometric modulators and produce a signal corresponding to thereceived light, wherein said computer is configured to receive thesignal from the detector, and based on the signal, to iteratively varythe length of time for applying the voltage waveform to identify aminimum time period during which the number of pixels have actuated orreleased during the determined time period meets a threshold value, andto determine one or more response time parameters based on the identicalminimum time period.
 63. The system of claim 62, wherein the one or moreresponse time parameters are based on the slowest actuation time orrelease time of one or more interferometric modulators.
 64. The systemof claim 62, wherein each of the plurality of interferometric modulatorscomprises a fixed reflective surface and a movable reflective surfacewherein the fixed reflective surface and the movable reflective surfaceare configured to cause interference of light.
 65. A system for testinga plurality of interferometric modulators, comprising: means fordetermining a time period during which to apply a switching voltagelevel, said switching voltage level being sufficient to change theinterferometric modulators between a non-actuated state and an actuatedstate, or an actuated state and a non-actuated state; means for applyinga controlled by said computer, said voltage source configured to apply avoltage waveform comprising the switching voltage level for the timeperiod; means for illuminating the interferometric modulators; and meansfor sensing light reflected from the interferometric modulators andproduce a signal corresponding to the received light, wherein saiddetermining means receives the signal from the sensing means anddetermines one or more response time parameters based on the signal, andsaid determining a time period means is further configured toiteratively control the application of a voltage waveform for adetermined time period to identify a minimum time period where thenumber of pixels have actuated or released during the determined timeperiod meets a threshold value.
 66. The system of claim 65, wherein theone or more response time parameters are based on the slowest actuationtime or release time of one or more interferometric modulators.
 67. Thesystem of claim 65, wherein said determining means comprises a computer.68. The system of claim 65, wherein said applying means comprises avoltage source.
 69. The system of claim 65, wherein said illuminatingmeans comprises a light source.
 70. The system of claim 65, wherein saidsensing means comprises a photo detector.
 71. The system of claim 65,wherein each of the plurality of interferometric modulators comprises afixed reflective surface and a movable reflective surface wherein thefixed reflective surface and the movable reflective surface areconfigured to cause interference of light.
 72. A method of manufacturinga system for testing a plurality of interferometric modulators,comprising: providing a computer configured to determine a time periodduring which to apply a switching voltage level, said switching voltagelevel being sufficient to change the interferometric modulators betweena released state and an actuated state, or an actuated state and areleased state; coupling a voltage source said computer, said voltagesource configured to apply a voltage waveform comprising the switchingvoltage level for the time period; positioning a light source toilluminate the interferometric modulators; and positioning a detector toreceive light reflecting from the interferometric modulators and producea signal corresponding to the received light, wherein said computer isconfigured to receive the signal from the detector, and based on thesignal, to iteratively vary the length of time for applying the voltagewaveform to identify a minimum time period during which the number ofpixels have actuated or released during the determined time period meetsa threshold value and to determine one or more response time parametersbased on the identical minimum time period.
 73. The method of claim 72,wherein each of the plurality of interferometric modulators comprises afixed reflective surface and a movable reflective surface wherein thefixed reflective surface and the movable reflective surface areconfigured to cause interference of light.